tedparis

Hey guys, while I've been out wheeling and when I'm driving on the road I notice how bad the U-Joints operate at high speed. I am looking to replace the U joints with CV shafts to eliminate the uneven rotating speed. For those of you that don't know, U joints have a flaw in there nature. They rotate at a changing angular velocity that becomes more sever as the angle they are experiencing increases. I am an intern studying to be an engineer and one of the challenges we have had is dealing with U Joints on our heavy duty trucks. The Jeep XJ I believe has 3 U-Joints that are not counteracted by another U-Joint. The front U-Joint that inputs to the front axle, and then the two U-Joints that feed the wheels on the front axle. The CV shaft was developed to eliminate this issue and although I am new to Jeeps I know this is a problem for me because I had to have my bevel gears replaced in my front axle I believe because of the changing velocities of the front differential and axle shafts.


What I want to know is can I put the front drive shaft and axle shafts from a front ZJ axle in my front XJ axle to eliminate this issue? I have a HP Dana 30 on my 98. I don't know what axle the ZJ has or is the drive shafts are swappable.

ohio95xj

Yes, you "can" swap them in. But they are weaker. Although I don't know why you would. With proper maintenance. This whole thing is a non issue, or minimal at best.

tedparis

Awesome, Do you know what years are compatible? I have a 98 that I want to swap the axle shafts in and the front drive shaft. Can I swap the front drive shaft from a ZJ to an XJ?

Atmos

aj2494

I wouldn't use the truck issues you've been having at work to justify the necessity of CV shafts. Completely different vehicle and geometry. It's not an issue at all, and CV joints are actually significantly weaker. There's an inherent issue with anything that rotates and involves angles, not just u-joints. I would highly suggest you not do this swap. It's the opposite of most of our goals (strengthen things), and I've never heard anybody complain that their perfectly good u-joints are causing vibes. I'm also not sure what you mean by "changing angular velocity", since no changing angular velocity would mean no acceleration.

aj2494

Just looked up what you're talking about. That is such a minimal effect that it's not even funny. This is what happens when you get technical knowledge and try to apply it to everything on your personal vehicle. There's a reason Jeep used u-joints from the factory, and there's a reason you're the first person I've ever seen ask about this. No offense to you at all, and I actually commend you on using your work experience to improve your XJ. This is just nitpicking though, and it won't get you or your XJ anywhere.

SatiricalHen

how can you notice how the u joints work at high speed if they aren't even driving anything or doing any work. They're just free spinning. I don't know what bevel gears are unless you mean spider gears in the carrier. I've never heard of this problem. If you're experiencing problems it might just be from the u joints being bad. Mine went bad and I could only tell they were bad when I was driving it front wheel drive only and turning. I don't think the cv joints are the solution to whatever problems you're having.

tedparis

I mainly just wanted to see how big of a difference it made when I went wheeling, I understand that it is considered negligible but when you get a chance putyour jeep in four wheel drive crank the wheel all the way to the right or leftand try to turn. Then get in a grand Cherokee and do the same thing andlet me know what you think because I think there is a difference but maybe its all in my head. I've been working with U-Joints for a long time and there's a reason that newer Jeeps have CV Shafts instead of U-Joints. Crawl under a 2015 2 door jeep and you'll see CV shafts driving the rear axle, they are still looking into changing the front over to CV's. They had a few prototypes down in the garage where I work that had CV axles instead of U-Joints. Like I said maybe its in my head but I want to see if it makes a noticeable difference when I turn in 4x4 drive.


I do appreciate your guys input! You might save me a lot of time and money if you convince me! That's why I posted this question.

SatiricalHen

its because we have part time 4wd and they have full time 4wd.

tedparis

I had bad u-joints in my Jeep and replaced them then the spider gears went bad 20,000 miles later so it very well could have been the bad U-Joints. Like I said its mainly just for an experiment to see if it makes a difference.

Atmos

someone has already come up with a solution

http://www.polyperformance.com/RCV-U...ep-TJ-XJ-YJ-JK

SatiricalHen

I've honestly never heard of spider gears even going bad. A u joint wouldn't cause that though. Only thing I could think of that would cause that is someone welding the spider gears to "lock" the axle then the welds breaking, or if you had sand, water or lack of gear oil in the differential. You're going backwards by replacing the u joints with cv joints. U joints are cheaper, easier, and stronger. The only cv type joint I would put in my jeep would be an rcv and those are really expensive.

tedparis

Right! Those are CV joints they are 1000 dollars, getting some Grand Cherokee Shafts will be a lot cheaper, I found some on craigslist for 50 dollars.

ohio95xj

Yes, but the grand Cherokee CV joints are notoriously weak. Bottom line. If you plan to wheel it at all, and you feel like you "Need" CV joints. RVC shafts are the only way to go. But like many have said. U-joints are perfectly fine for our jeeps.

tedparis

Alright! Well I am glad I asked you guys then, maybe I will keep the U-Joints on my Wheeler then and put the CV shafts on my daily driver since I only use it when I am in snow and rain anyway, so I don't have to worry about strength so much.